What are neural tube defects?

Neural tube defects (NTDs) are birth defects. They are a group of disorders that arise early in pregnancy that affect the development of a baby and can cause life-long complications of varying severity.

During the first 3 to 4 weeks of a pregnancy, specific cells in a developing baby curl up and their edges fuse together to form a narrow tube that becomes the foundation of the spinal cord, brain, and the bone and tissues that surround them. This neural tube fusing process usually is complete by 28 days of pregnancy (gestation), before many women even know that they are pregnant. A neural tube defect occurs when the tube does not close properly somewhere along its entire length.

Normally, the spinal cord and brain are surrounded and cushioned by cerebrospinal fluid (CSF) and are protected by outer layers of tissue called the meninges. The brain is further protected by the skull, and the spinal cord is protected by the bones of the spine (vertebrae), which form a flexible protective armor of bone. When someone has a NTD, there are one or more gaps in the brain or spinal cord's protection. This can affect the brain's development and can leave the spinal cord vulnerable to damage. Because the spinal cord contains the nerves that control body movements and functions, any damage that occurs can paralyze or weaken associated muscles and organs. The type of NTD that develops, its severity, its affect on fetal development, and its potential for future complications will depend upon where the defect is and what tissues are involved.

The cause of NTDs is not known. Scientists believe that there are genetic, environmental, and nutritional components. According to the March of Dimes, neural tube defects happen in about 3,000 pregnancies each year in the United States. About 1,500 babies are born in the U.S. with spina bifida, the most common NTD, according to the National Institute of Child Health and Human Development. Less commonly, encephalocele affects about 340 infants, and about 860 are born with anencephaly.

Some factors that increase the risk of having a baby with an NTD include:

Personal history—people who have an NTD or a child diagnosed with NTD

Family history—people who have family members with an NTD

Use of some anti-seizure medications, such as valproic acid, have been associated with an increased risk. A woman should discuss her medications with her healthcare provider before becoming pregnant.

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This article was last reviewed on November 14, 2014. | This article was last modified on December 29, 2014.

The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.

The modified date indicates that one or more changes were made to the article. Such changes may or may not result from a full review of the article, so the two dates may not always agree.